public class test2_merge {
    // https://leetcode.cn/problems/sort-an-array/
    int [] tmp;
    public int[] sortArray(int[] nums) {
        tmp=new int[nums.length];
        mergeSort(nums,0,nums.length-1);
        return nums;
    }
    public void mergeSort(int[] nums,int left,int right) {
        if(left>=right) return;
        // 1.根据中间点将数组分成两部分
        int mid=(left+right)/2;
        // [left,mid],[mid+1,right]
        // 2. 先把左右区间排个序
        mergeSort(nums,left,mid);
        mergeSort(nums,mid+1,right);
        // 3. 合并两个有序数组
        int cur1=left,cur2=mid+1,i=0;
        while(cur1<=mid && cur2<=right) {
            tmp[i++]=nums[cur1]<=nums[cur2]?nums[cur1++]:nums[cur2++];
        }
        // 处理没有遍历完的数组
        while(cur1<=mid) tmp[i++]=nums[cur1++];
        while(cur2<=right) tmp[i++]=nums[cur2++];
        // 4. 还原
        for(int j=left;j<=right;j++) {
            nums[j]=tmp[j-left];
        }
    }
}
